Molecular sieve adsorbents



'ural zeolites. 'pear to be appropriately applied to the materials of the MOLECULAR SIEVE ADSORBENTS Robert M. Milton, Bnlfalo, N.Y., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Application December 24, 1953 Serial No. 400,388

24 Claims. (Cl. 252-455) This invention relates to synthetic adsorbent materials and, more particularly, to a synthetic crystalline form of g sodium aluminum silicate, its derivatives, and methods of making and activating these adsorbent materials.

It is the principal object of the invention to provide A further object is to provide a tion is to provide a synthetic material having unique ladsorptive properties and a high adsorptive capacity.

Another object of the invention is to provide a convenient and efficient method of making and activating the novel adsorbent of the invention.

Naturally occurring hydrated metal aluminum silicates are called zeolites, and the synthetic materials of the invention have compositions similar to some of the nat- Accordingly, the term zeolite would apinvention. There are, however, significant difierences between the synthetic and natural materials. the one from the other the material of the invention, synthetic crystalline sodium aluminum silicate and its derivatives, will be designated hereinafter by the term zeolite A.

Certain adsorbents, including zeolite A, which selectively adsorb molecules on the basis of the size and shape of the adsorbate molecule are referred to as molecular sieves. These molecular sieves have a sorption area available on the inside of a large number of uniformly sized pores of molecular dimensions. With such an-arrangementmolecules of a certain size and shape enter the pores and are adsorbed while larger or differently shaped rnolecules are excluded. Not all adsorbents behave in the manner of the molecular sieves. Such common adsorbents as charcoal and silica gel, for example, do not exhibit molecular sieve action.

Zeolite A consists basically of a three-dimensional framework of SiO -and A tetrahedra. The tetrahedra are cross-linked by the sharing of oxygen atoms so that the ratio of oxygen atoms to the total of the aluminum and silicon atoms is equal to two or O(Al-|-Si)=2. The

'electrovalence of the tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example, an alkali or alkaline earth metal ion. This balance may be expressed by the formula Al (Ca, Sr, Ba, Na K )=l. One cation may be exchanged for another by ion exchange techniques which are described below. The spaces between the tetrahedra are occupied by watermolecules prior to dehydration.

Zeolite A may be activated by heating to effect the loss of the water of hydration. The dehydration results in crystals interlaced with channels of molecular dimensions that offer very high surface areas for the adsorption of foreign molecules. accept molecules that have a maximum dimension of the These interstitial channels will not minimum projected cross-section in excess of about 5.5 A. Factors influencing occlusion by the activated zeolite To distinguish Un t d States Patent O e 2,882,243 Patented Apr. 14,. 1959 A crystals are the size and polarizing power of the interstitial cation, the polarizability and polarity of the occluded molecules, the dimensions and shape of the sorbed molecule relative to those of the channels, the duration and severity of dehydration and desorption, and the presence of foreign molecules in the interstitial channels. It will be understood that the refusal characteristics of zeolite A are quite as important as the adsorptive or positive adsorption characteristics. For instance, if water and another material are to be separated, it is as essential that the crystals refuse the other material as it is that they adsorb the water.

A feature of the invention is the relatively simple process by which the zeolite A may be prepared. Although there are a number of cations that may be presentin zeolite A it is preferred to' formulate or synthesize the sodium form of the crystal since the reactants are readily available and water soluble. Thesodium in the sodium form of zeolite A may be easily exchanged for other cations as will be shown below. Essentially the preferred process comprises heating a proper mixture in aqueous solution of the oxides, or of materials whose chemical compositions can be completely represented as mixtures of the oxides, Na O, A1 0 SiO and H 0, suitably at a temperature of about 100 C. for periods'of time ranging from 15 minutes -to' hours or longer. The product which crystallizes from the hot-mixture is filtered off and washed with distilled water until the chinent wash water in equilibrium with the zeolite has a pH of from about 9 to 12. The material, after activation, is

characteristics that are useful in identifying zeolite A are its composition and density.

The basic formula for all crystalline zeolites where M" represents a metal and n its valence may be represented as follows:

M 0 A1 0 XSiO YH O In general a particular crystalline zeolite will have values for X and Y that fall in a definite range. The value X for a particular zeolite will vary somewhat since. the aluminum atoms and the silicon atoms bothvoccupy essentially equivalent positions in the lattice. Minor. variations in the relative numbers of these atoms do not significantly alter the crystal structure or physical properties of the zeolite. For zeolite A, numerous analyses have shown that an average value for X is about 1.85. The X value falls within the range 1.85 :05.

The value of Y likewise is not necessarily an invariant for all samples of zeolite A particularly among the various ion exchanged forms of zeolite A. This is true because various exchangeable ions are of different size, and, since there is no major change in the crystal lattice dimensions upon ion exchange, more or less space should be available in the pores of the zeolite A to accommodate water molecules. For instance, sodium zeolite A was partially exchanged with magnesium, and lithium, and the pore volume of these forms, in the activated condition, measured with the following results:

"The average value*forYthus determined for the fully hydrated sodium -zeolite 'A "was 5 1 and in varying conditions of hydration, the value of Y can vary from 5.1 to essentially zero. The maximum value of Y has been '?fo'undin75% "'exchangedmagtiesium zeolite Afithe fully hydratedformof' which hasa' Y value of 5:8. "In general "a'n increase in the-degree 'of' 'i'on exchange er thef-magneium form'ofzeolite A results in=an increasein"the"Y value. Earg'erwalues, up to-"6, "may 'be-obtai'rie'd with "*more'fdlly 'ionex'change'd' materials.

In zeolite A synthesized according-to the preferred "procedure/the ratio Na o/ A1 I shouldequal one. 'But if an of the *excess' alkali present in the m'other'liquor 'isnot washed- 'o-ut--'of the precipitated "product, analysis "may'showW-ratio greatefithan'onefaridif the washin'gis carried too far, some sodium may be ion' exchariged' by hydrogen/and the ratio will" drop""below one. Thus, a 'tpical-"analysis for a "thoroughlywashed' soditli'lm zeolite K991 121 051.0A1503E1i858ig05' IHQO. Theseus 'aGfA-lgO hasvaried as -much"-as 2 3 Theco'mipesinsn for' z'eolit'e A lies in the' 'r'ange-Of whereM represents a metal and ii 'its valence. [Thus l the iformulafforzeolite A may be written-as Tollows:

1:0 502M1 0:?Al O :.1 ;85=:l: 0:5Si'O i YH O 'I'L f'Inthis*formula M represents a metal, it its valence, and Y may the anyvalue up 't'06 depending "on the identity 'ofthe'metal 'an'dthe degree of dehydration of the crystals. I

"Thep'ores'of zeolite A are 'normally 'fill'edwith water and in this "case, the above formula represents 'their chemical analysis. When other materials as well' as Water are'in the pores "of zeolite A, 'chemical"analysis 'will-hdw-"a lower value of Y'and 'theipresen'ce of other adsorbates. The presence'in the pores of non-volatile materials, such'assodium chloride and sodium hydroxide, which are not removable under normal conditions of activation at temperatures of from 100 C. to 650 C. does not significantly alter the crystal lattice or structure of zeolite A although it will of necessity alter the chemical composition.

The apparent density'o'f fully hydrated samples of zeolite were determined by th'e "notational? the crystals one-liquids of appropriate densities. The technique and liquids-used are discussed in an article e'ntitl'e'd Density of Liquid Mixture appearing in Acta -'Crystallographica, .1951, vol. -4,.page 565. The densities of several such crystals are as .follows:

Percent of Density,-"g;/cc. exchange Form of zeolite A '1.99i0.1. 1.92=!=0.1. 2.08:l:0.1. 2.26:5:01. 2.04i0.1. 2.05=|:0.1.

About 3.36.

"results have nearest-amid with "the temperatureofthe suitable heating apparatus, for example an ov'enf'satid and the reactants heated for the required time. A con- "venientand preferred procedure forpreparing therea'ctant mixture is to make an aqueous solution containing the sodium aluminate and hydroxide and add this, preferably with agitation, to an aqueous solution of sodium silicate. The system is stirred until homogeneous or until any gel which forms is broken into a nearly homogeneous mix. After this mixing, agitation may be stopped as it is'unnec'essary to agitate there-acting mass during the formation and crystallization of the-zeolite, however, mixing during formationandcrystallization'has not been found to be detrimental. The initial mixing of ingredients'is conveniently'done at room temperaturehut this is not essential.

A crystallizationtemp'erature of about C. has been found to be particularly advantageous in this process. The temperature is easy to maintain. It is high enough to eifectively promote the reaction and yet low enough activation, have'a nigh'aasorbin gespait Satisfactory reaction as low as about'2l" -C.a'n'd"as highasabout -C., the pressure being atniosplrelricor atle'astthat "corresponding to 'thevapor ipre'ssur'ebfwater in"e'quilibri'um with themixture at the highertempe'rature. "Any bath, oil bath, or jacketed'autoclavernay'be used. For convenience, in laboratory work, glassvess'els containing "the reactantsare heldimmersed in abath'of boiling'water "giving a temperature "of about 10 0 C. 'In quantity production, steam jacketed Ves's'elso'ifer a "convenient means of controlling the temperature. For't'er'n'pefat'iires between roomtemperature (21 C.) and 150 'C., increasing the reactiontemperature increases the rate of feactio'nand decreases thereaction 'p'e'riod. Forexample, sodium zeolite A is'obtainedin-Gdaysat 21 C.,' in about 45 'r'ninut'esat IOO" C., andfevenfasterat 150C. Qnce "the' zeolite crystals have formed they 'main'tainftheir structure, and holding the reaction temperatur'efor a longer time than is necessary 'for themaxii'niiiniyieldof crystals "does no harm. For instance, zeolite A which may be completely crystallized within 6 "hours at'1 0 C. can remain in contact with the mother liquor 'at"'100 'C.'-for 'an'additiorral 50 to 100 hou'rsw'ith no'appa'rent change in yield or crystal structure. 7

After the reaction period, the' zeolite crystals are filtered off. The reaction magma 'may efilteredatthe reaction'temp'erature if desired buthot magmasare pref- 'erably"cooled "to room temperature before filtering. The "filtrate, orfrnother liquor, may be reused 'afterenrich- "mentwiththeproper am'ounts'o'f reactants to giv afp'rf o'p- *erly proportioned reactant mixture. The mass of "zeolite crystals is washed (preferably "with distilled "water-and "conveniently in "the filter)until the efflue'nt 'wssh'water, in equilibrium with the zeolite has a pH 'of between Thereafter, thecr'ys'ta ls are 'dried, "convenientl'ydn 'a and 150 C. For X-ray "and chemiealanalysis, this drying is suflicient. In practical usefthere'ne'ed 'b'en'o separate drying stepfas the zeolites'will dry 'as they 'a'i'ea'cti- -vated. The individual crystals of the 'synthetic'z'eolite A usually appear'to be cubic. Most of the crystals have a "size "in =the'ran'ge"0.l micron to 10'mic'rons, but smaller and 'la'rger crystals can 'occur covering 'the size range of 0.01 micronto 1 00 microns.

In thesynthesis 'of zeolite A, it hasbee'n foufidfthat the composition of the reacting "mi'xture'i's critical. The 'crystallizing temperature and the length of "time the c'rystallizing temperature is maintained are important "variables in determining the yield of crystalline material.

Under some conditions, fo'rex'am'ple too low a tempera- Specific examples of the production of the sodium form of zeolite A are given in Table 1 below. The mixtures and treatments described resulted in essentially pure crystalline zeolite A except in runs 12 and 13 in which Zeolite A has also been produced, in admixture with other crystalline sodium aluminum silicates and crystalline alumina, from reactants in proportions outside the from 5% to of another crystalline form of sodium 5 aluminum silicate was mixed with the zeolite A. In run 3 and subsequent runs the term solution S refers to a water solution of sodium silicate containing approximately 7.5% by weightt Na O and 25.8% by weight SiO 10 TABLE I Ratio of oxides Run Reactants Temp. Dura- No. 0.) tion (hrs) 8102/ No.20} 1120/ 15 A120: on NazO 1. 30 gm. silica e1+41 100 92 1.8 0.56

gm. NaAl0r+excess water to a pH of about 13.5

2 1 part by weight 100 76 2.0 0. 5

N aAl0r+0.92 part by weight slliclc acid+water to a pH of about 13.5.

3.-." so gm. NaAlOz+126 100 12 1.2 1.2

gm. Solution S"+320 cc. H20.

4..-" 15 gm. NaAl02+ 100 39 1.0 1.5 37

10.7 .Solution S"+1. 7 gm.

5 15 gm. NaAlO2+9.8 100 0.5 3.2 37

gm. Solution S" 30 +2.5 gm. NaOH +83 cc. H20.

e 45 gm. NaAlOz+63 25 t 14 1.1 1.3

gm. "Solution S" +100 cc. H20.

7 gm. alumina tri- 100 48 1. 2 1. 4 87 hydrate+18.5 gm.

"Solution s"+7.4 gm. N8OH+55 s 150 gm. NaAl0a+ 100 1 1.2 1.2 43

23.3 gm. "Solutlon S+75.0 cc.

s 9 gm. NaAlOH-ZBA 100 as 2.0 2.0 50

gm. "Solution S" +9.7 gm. NaOH 197 cc. H20

10.... 1795511. NaAlOz+ 100 62 1.7 0. 95 52 39.4 gm. Solution s"+125 cc.

1 ao 'N A10 +47 120 s 1- 2 1 2 4 Solution S" 5 +125 gm. H20.

12.... 11.4 gm. NaAlOz, 150 2% 1.2 1.2

17.9 gm. Solution S", 47.6 gm.

1?. SO N A10 455 112 1 2 1 4 3e 5% Solution S", 50 150 gm. H20, 4 gm. NaOH.

1 Days.

The sodium form of zeolite A has been produced at 55 100 C., essentially free from contaminating materials, from reacting mixtures whose compositions, expressed as mixtures of the oxides, fall within either of the following ranges.

Range 1 Range 2 Sl02/A1z0a 0. 5-1. 3 1. 3-2. 5

Nero/S10 1. 0-3.0 0.8-3.0

Ego/N840 35-200 35-200 Range 1 Range 2 slog/1.1.0. 0. 06-3. 4 doe-3.4 Nam/$0,. 0. 7-s. 0 3.0-20 Ego/No.10 4-3 4-60 Similarly zeolite A, mixed with still another crystalline form of sodium aluminum silicate, has been produced by holding at C. reaction mixtures whose compositions, expressed as oxide ratios, fall within the following range.

SiO A1 0 1.5-3 .0 Na O/SiO 0.9-1.5 H 0/Na 0 35-200 Similarly, zeolite A mixed with crystalline alumina trihydrate has been produced at 100 C. from reaction mixtures whose compositions, expressed as oxide ratios, fall within the following range.

SiO /Al 0 Nago/siog H O/Na O 39-50 SiOg/ A1 0 Na O/SiO 1.8 HBO/N320 When zeolite A has been prepared, mixed with other materials, the X-ray pattern of the mixture can "be "reproduced by a simple proportional addition of the X-ray patterns of the individual pure components.

Other properties, for instance molecular sieve selectivity, characteristic of zeolite A are present in the properties of the mixture to the extent that zeolite A is p of the mixture.

The adsorbents contemplated herein include not only the sodium form of zeolite A as synthesized above from a sodium-aluminum-silicate-water system with sodium as the exchangeable cation but also crystalline materials obtained from such a zeolite by partial or complete replacement of the sodium ion with other cations. The sodium cations can be replaced, at least in part, by other ions. These replacing ions can be classified in the following groups: other monovalent or divalent cations, such as lithium and magnesium; metal ions in group I of the periodic table such as potassium and silver; group 11' metal ions such as calcium, and strontium; metal ions of the transition metals such as nickel; and other ions, for example, hydrogen and ammonium, which with zeolite A behave like metals in that they can replace metal-ions without causing any appreciable change in the basic structure of the zeolite crystal. The transition metals are those whose atomic numbers are from 21 to 28, from 39 to 46 and from 72 to 78 inclusive, namely, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, yttrium, zirconium, niobium, molybdenum, ruthium, rhodium, palladium, hafnium, tantalum, tungsten, rhenium, osmium, iridium and platinum.

The spatial arrangement of the aluminum, silicon and oxygen atoms which make up the basic crystal lattice of the zeolite remains essentially unchanged by partial or complete substitution of the sodium ion by other cations. The X-ray patterns of the ion exchanged forms of the zeolite A show the same principal lines at essentially the same positions, but there are some differences in the relative intensities of the X-ray lines, due to the ion exchange.

Ion exchange of the sodium form of zeolite A (which for convenience may be represented as Na A) or other forms of zeolite A may be accomplished by conventional ion exchange methods. A preferred continuous method is to pack zeolite A into aseries of vertical columns with suitable-supportsat thebottom; successively pass through hebeds a watersolution of a soluble salt of the cation to beintroduced. into the zeolite; and, change the flow from the, first bed to the second bed as the zeolite in the first bed becomes ion exchanged to the desired extent.

To obtain hydrogen exchange, a water solution of an acid'such as hydrochloric acid is efiective as the exchang- -ing solution. For sodium exchange, a water solution of sodium chloride is suitable. Other convenient reagents are: for'potassium exchange, a water solution of potassium chloride or dilute potassium hydroxide (pH not over about 12); for lithium, magnesium, calcium, ammonium, ;nickel or strontium exchange, water solutions of the chlorides of these elements; for zinc exchange, awater solution of zinc nitrate; and for silver exchange, a silver nitrate solution. While-it is more convenient to use water soluble compounds of the exchange, cations, other solutions containing the'd'esired' cations or hydrated cations may be used.

Inzatypical case of batch-wise exchange, a solution of 7.8 grams of calcium chloride in 750 cc. of distilled water was added with stirring to a beaker containing 25 grams of hydrated sodium zeolite A (Na A). After four days: at room temperature the supernatant liquid was decanted-and another 750 cc. of distilled water containing 718*grams; of calcium chloride was added with stirring. After one day at room temperature the supernatant liq uid was again decanted, and another 750 cc. of distilled water containing 7.8 grams of calcium chloride was added :with stirring. One day later the supernatant liquid was 'decanted and 750 cc. of distilled water was added with stirring. After another day at room temperature this Supernatant liquid was again decanted and the zeolite A dried. Chemicallanalysis of the exchanged zeolite showed added, A day later this process was repeated, and after still another day, the supernatant liquid was again decantedand 750 cc ofdistilled water added. The chemical analysis; of; the, zeolite A so exchanged showed that 91% of thesodiumions had been replaced with potassium, ions.

.In a; column, exchange, 33v grams-of sodium zeolite A Na A) were-packedinto a glass; column having a diameter-of'two centimeters and a fritted glass disk as a bottom support for the zeolitebed. A solution made by dissolying;10;grams of calcium chloride in two, liters of dis.- tilled; water was passed through the bed. After passage of t-hesolution, thezeolitewasremoved from the column and jd ried, Chemical analysis showed that 66% of the isodiutn ion'shad been replaced by calcium ions.

The-extent to which ion exchange occurs may be controlled. Forinstance, calcium exchange for sodium has beeneffected in a mounts; of from or less to complete replacement of the sodium ion. One procedure for controlling the degree of exchange is to, soak a known quantity of s odium zeolite A in solutions containing predetermined amounts of exchangeable ions. -In one series of experiments with sodium zeolite A and calcium ions, when the totahcalcium available in the solution was 5% of the amount which; could enterthe zeolite A if all the sodium were replaced, it. was found that 5% of the sodium ions actuallyvwere replaced inZO minutes contact time at room temperature. When the exchange solution contained 60% ofgthe theoretical amount of calcium required for complete exchange, 47% of the sodium ions were actually replaced inm minutesatroom temperature. Using three times theamou,nt of ;=calcium theoretically required to make a .comp eteexchangerthe placementof 77%; of. the so ium 8 ions actually took place at room temperature within 20 minutes. .More'complete exchange can be obtained if the temperature is raised to C. or if the exchange operation is repeated several times by replacing the spent exchange solution with a fresh solution. A completely exchanged calcium zeolite A (CaA) is obtained by a combination of heating and repeating the exchange operation.

The rate of exchange of sodium zeolite A can under some conditions be quite'rapid. For instance, when sodium zeolite A was put into a solution 0.1 molar in calcium ions, 47% of the sodium ions were replaced in a two minute contact time at 25 C., and in 7 /2 minutes the exchange was 59% complete. Under these conditions of solution concentration, about 60% was the maximum exchange achievable.

Hydrogen ion exchange of zeolite A is obtained by treating the zeolite A with water or acid. When sodium zeolite A is put into distilled water, the pH rises to between about 10 and 11 indicating that hydrogen ions from the water enter the lattice and displace some sodium ions. This displacement occurs according to the following equation:

Four grams of sodium zeolite A, (Na A) in 60 cc. of water, gave an equilibrium pH of 10. When sodium chloride was added to the mixture of water and sodium zeolite A thev pH fell. On adding enough sodium chloride to the above equilibrium to make a 0.01 M solution, the pH dropped to 9. Still further addition of sodium chloride reduced the pH to 8.3 indicating a mass action etiect of the sodium chloride on the equilibrium.

To hasten and to effect more completely the hydrogen ion exchange, an acid should be substituted for the water. Uponaddition of increments of aqueous hydrochloric acid to a mixture of sodium zeolite A and water, the pH of the water solution fell steadily from 10% to about 3.8. Further additions of acid gave no further lowering of the pH value, and a good zeolite A X-ray pattern was shown by the product.

The pH of dilute hydrochloric acid to which sodium zeolite A powder is added rises from about 1 to about 3.8 after which the pH remains constant. In one case 550 cc. of a 0.1 normal solution of hydrochloric acid was added to 10 grams of sodium zeolite A in small increments. Upon the slow addition of the first cc., the pH rose to about 3.8. Upon the addition of the remaining 440 cc.,

no further change in pH was noted and X-ray examination of the product showed a strong zeolite A pattern.

When the amount of acid added to sodium zeolite A supplies the theoretical amount of hydrogen ion to completely replace the sodium ions, the product is primarily hydrogen exchanged zeolite A. If acid is added in excess of the amount theoretically required to permit complete exchange, the zeolite structure is destroyed, but the pH remains at about 3.8 throughout the process. For instance, 275 cc. of 0.1 normal solution of hydrochloric acid was added to 5 grams of sodium zeolite A. Thiswas approximately the theoretical amount of acid to give complete hydrogen exchange. Then 200 cc. more of the solution was added. The pH remained at 3.8. X-ray analysis showed a complete destruction of all crystal structure.

Hydrogen exchanged zeolite A may in turn be exchanged to sodium zeolite A, at least partially, by adding dilute sodium hydroxide to hydrogen zeolite A. X-ray and adsorption tests show the material so treated to contain sodium zeolite A.

Among the ways of identifying zeolite A and distinguishing it from other zeolites and other crystalline substances, the X-ray powder diffraction pattern has been found to be a useful tool. In obtaining the X-ray diffraction powder patterns, standard techniques were employed. The radiation was theKa doublet of copper, anda Geiger counter spectrometer with a strip chart pen recorderwas used.- The peak heights, I, and the positions as a function 1 TABLE A (Cont'd) of 20, where is the Bragg angle, Were read from the spectrometer chart. From these, the relative intensities, 4 N 1 m 1001 5315. (h=+k=+u) 1nd o d 50 0 d 11 vlalue, 3 5 0 0 11501 Where I 1s the mtenslty of the strongest l1ne or peak, and I 0 Em d (obs) the interplanar spacing in A., corresponding to the recorded lines were calculated. 6 1.053 s 1. 091 7 0. 001 X-ray powder difiraction data for a sodium zeolite A 2 4 1. 593 3 1. 631 7 0. 001 (Na -A), a 95% exchanged potasslum zeolite A (K A), 6 1.565 3 1.003 6 0.001 a 93% exchanged calcium zeolite A (CaA), a 94% ex- 62 fig, g 576 8 8-83} changed lithium zeolite A (Li- A), a 93% exchanged 05 1. 523 2 1.492 3 0.001 strontium zeolite A (SrA), and an exchanged thallium 516 1 {$5 g 388% zeolite A (TlA) are given in Table A. The table lists 1.459 2 1.493 7 0.001 the 100 I/I and the d values in A. for the observed line 3 i 388% for the difierent forms of zeolite A. The X-ray patterns 4 0.001 indicate a cubic unit cell of a of between 12.0 and 12.4 A. g 6 3:88; In a separate column are listed the sum of the squares g 0.001 of the Miller indices (h +k +l for a cubic unit cell 8 8133i that corresponds to the observed lines in the X-ray diffrac- 1 tion patterns. The a values for each particular zeolite 123M032 are-also tabulated and in another column the estimated errors in readin the osition of an X-ra eak on the g P y p 25 03A SrA Tl A Estispectrometer chart appear. I 1 mated The relative intensities and the positions of the lines are I error m+k +l=) 1n 5 only slightly d1frerent for these vanous 1on exchanged 1001/10 4 1001/10 4 1001/10 value. forms of zeolite A. The patterns show substantially all DIETS or of the same lines, and all meet the requirements of a cubic mums unit cell of approxrmately the same size. The spat 1al 12% 100 1136 90 1231 13 0.02 arrangement of s1l1conoxygenand aluminum atoms, 1.e. 8,00 39 2 06 8. 71 3 0. 02 the arrangement of the A10 and SiO.; tetrahedra, are 3 3 2% $2 3 8% essentially identical in all the forms of zeolite A. The 5143 I 0101 appearance of a few minor lines and the disappearance 4 4 g-gi of others from one form of zeolite A to another as well "4:63" 35 4111 7 01004 as slight changes in the intensities and positions of some 3875 2 3. 095 34 3. 714 60 3. 717 34 0. 003 of the X-ray hnes can be attnbuted to the difierent s1zes 3.539 4 3.556 15 3. 55s 13 0. 003

and numbers of canons present 1n the various forms since g 8- these differences effect some small expansion or contrac- 31031 01002 1 32 2. 100 2.990 22 0.002 of the crystals: 9 2.903 as 2. 906 6 0. 002 2.323 1 0.002 TABLE} A g 2. 753 49 2. 757 51 g. 24 2.025 49 2. 030' ""ii 01002 7 2.517 55 0.002 .5235 1 g-ggg g g-ggg (h -i-k -H iii? 3 83 a 100 a 100 a 100 value, 3 8- 8 1/10 1/15 I/Io pluhs1 or 7 002 m us 59 3.51 72 s. 71 04 0.02 001 6.96 42 7.10 30 0.01 0'001 0.15 4 0.01 001 25 5.39 25 5.50 10 0. 01 0-001 2 5.03 s 0. 01 dam 6 4.26 18 0. 01 30 4.02 48 4.105 33 0.004 7 M01 3. 305 4 3. 395 10 0. 003 001 53 3.033 53 3.714 02 0. 003 0-001 3. 555 5 0. 003 001 16 3. 342 23 3.414 34 0.003 6001 47 3.222 49 3. 292 35 0. 002 0-001 3. 07s 12 0. 002 001 2.923 43 2. 935 30 0. 002 6002 9 2. 337 4 2. 902 27 0. 002 0-002 12 2.691 4 2. 753 0. 002 6002 4 2.628 13 2.687 9 0. 002 01002 22 2.509 32 2.625 13 0. 002 0-002 5 2.457 7 2.514 23 0. 002 0-002 4 2. 40s 1 0. 002 0-002 2.363 9 2.415 4 0.002 0-002 3 2.319 5 2.370 9 0. 002 6002 1 2.235 3 2. 237 3 0. 002 6002 3 2.199 3 2. 243 5 0. 002 3 6002 7 2.177 26 0. 002 9 23 3 12 s- 91 4 5 "g- 001 no 12.26;l;0.02 12.32=|=0.02 12.33=|;0.02 9 2.007 20 2.053 3 0. 001

iii i "1555 "1' 9133i 1:881 8 1 7 j 001 In the above table, particularly with reference to SrA, 1.859 2 g 838% certain values have not been listed since their calcula- 3 795 2 0:001 tion was not necessary in the determination of the di- 2 3 M01 mensions of the unit cell. The dimension of the edge 13 1.702 10 1.742 12 0. 001 1,686 1 M01 .75 of the wine unit cell of the magnesmm zeohte A was 1 'pher in establishing identities.

11 obtained from data not tabulated above and is 12.29 A.:0.02A.

The more significant d values for zeolite A are given in Table B.

TABLE B d Value of reflection in A.

Zeolite A may be defined as a synthetic crystalline aluminum-silicate having an X-ray powder difiraction pattern characterized by at least those reflections set forth in Table B.

Occasionally, additional lines not belonging to the pattern for zeolite A, appear in a pattern along with the X-ray lines characteristic of zeolite A. 'This is .an indication that one or more additional crystalline materials are mixed with zeolite A in the sample being tested. Frequently these additional materials can be identified as initial reactants in the synthesis of the zeolite, or as other crystalline substances. When zeolite A is heat treated at temperatures of between 100 and 600 C. in thepresence of water vapor or other gases or vapors, the relative intensities of the lines in the X-ray pattern-may be appreciably changed from those existing in the unactivated zeolite A patterns. Small changes in line positions may also occur under these conditions. These changes in no way hinder the identification of these X-ray patterns as belonging to zeolite A.

The particular X-ray technique and/or apparatus employed, the humidity, the temperature, the orientation of thepowder crystals and other variables, all of which are well known and understood to those skilled in the art of X-ray-crystallography or diifraction can cause some variationsin the intensities and positions of the lines. These changes, even in those few instances where they become large, pose no problem to the skilled X-ray crystallogra- Thus, the X-ray data given herein to identify the A lattice are not to exclude those materials which, due to some variable mentioned or otherwise known to those skilled in 'the art, fail to show all of the lines, or show a few extra ones that are permissible in the cubic system of the A zeolite, or show a slight shift in position of the lines, 'so as to give a slightly larger or. smaller lattice parameter.

The zeolites contemplated herein exhibit adsorptive properties that are unique among known adsorbents. The common adsorbents, like charcoal and silica gel, show adsorption selectivities based primarily on the' boiling point or critical temperature of the adsorbate. Activated zeolite A on the other hand exhibits a selectivity based on the size and shape of the adsorbate molecule. Among those adsorbate molecules Whose size and shape are such as to permit adsorption by zeolite A, a very strong preference is exhibited toward those that are polar, polarizable, and unsaturated. Another property of zeolite A that contributes to its unique position among adsorbents is that of adsorbing large quantities of adsorbate either at very low pressures, at very low partial pressures, or at very low concentrations. One oracombination .of one or more of these three adsorption characteristics or others can make zeolite A useful for numerous gas or liquid separation processes where adsorbents are not now employed. The use ofzeolite A permits moreeffici'entand more economical operation of'numerous processes now employing other adsorbents.

- Qommonladsorbents; like silica gel and. charcoal donut exhibit any a reciable molecular sieve ction. where s the various forms Qfizeqlite Ado. This .is shown in the following tables for typical samples of the adsorbents. In these tables as well as others in the specification the term Weight percent adsorbed refers to the percentage increase in the'weight of the adsorbent. The adsorbents were activated by heating them at a reduced pressure to remove adsorbed materials. Throughout the specification'the'activation temperature for zeolite A was 350 C. and the. pressure at which, it was heated was lessv than about 0.1 millimeter of mercury absolute unless otherwise specified. In Tables II, III, and IV the activation temperature is given .for each sample. Throughout the specification, unless otherwise indicated, the pressure given for each adsorption is the pressure of the adsorbate at the adsorption conditions.

TABLE II Weight percent adsorbed at 259 C. and at 760 mm. Hg Activation Adsorbent temperature, C. Methane Ethane Propane .p. {b.p. {b.p.

-161.5 C.) -88.3 O.) -44.5 C.)

Charcoal 350, 2. 5 10, 1 17. 6 Silica gel 175 0. 5 1. 6 6. 3 Sodiumizeolite A..." .350 1. 6 8. 0 l. 2

TABLEv HI Welghtpercent adsorbed at I96 0. Activation, Adsorbent temperature, 0. Oxygen at Nitrogen 7 mm. at 100mm,

e He Charcoal 300 44 40 Silica gel 1'75 19. 9 24. 9 Sodium zeolite A 350 2,4.1 0.6

TABLE IV 7 Weight percent adsorbed. at 25 C. Activation Adsorbent temperature, C. n-Butanoi i-Butanol at 6 mm. at 12 mm. Hg Hg Charcoal 350 52. 2 50.1 Silica gel 17,5 33; 2 34. 0 Magnesium zeolite A (ov er 50% exchanged) 350 .10. 3

TableII demonstrates the fact that charcoal and silica gel-show a preference, toward thestraight chain saturated hydrocarbons in the order of their boilingpoints, adsorb.- ingthe-higher boiling propane more strongly than the lower'boiling ethane and methane. The. sodium zeolite A exhibits molecular sieve action and almost entirely excludes the larger propane molecule, yet permits the adsorption of ethane and methane. The methane. is less strongly adsorbed than the ethane by zeolite A at this condition of pressure and temperature because ofiits low boiling point. These data show the feasibility of using sodium zeolite A to separate methane .and ethane from mixtures with propane. Zeolite A "may also be used to separate methane and ethane from mixtures Of these hydrocarbons with higher homologs of the methane-ethane series and also from molecules that have maximum dimensions of their minimum projected cross-sectional area larger than that of propane, such as cyclic molecules. havingfour or more atoms in the ring, and from gasesthat are not appreciably adsorbed at room temperature because of their extremely high 13 volatility or low boiling point, suchas helium, hydrogen, nitrogen and oxygen.

Table III shows that charcoal and silica gel adsorb oxygen and nitrogen at liquid air temperatures. The sieving characteristic of sodium zeolite A prevents appreciable adsorption of nitrogen, yet permits adsorption of the smaller oxygen molecule.

Table IV illustrates the lack of appreciable selectivity shown by charcoal and silica gel between normal butanol and iso-butanol. The magnesium zeolite A, however, adsorbs very long straight chain hydrocarbon and alcohol molecules, such as normal butanol, but not appreciable amounts of branched chain molecules, such as iso-butanol.

Potassium zeolite A obtained from other forms of zeolite A by exchange with a water solution of potassium chloride has a small pore size as shown by the fact that of a large number of adsorbates tested only water was adsorbed to any appreciable extent. The following table lists adsorption data for a representative sample of potassium zeolite A (K A) prepared from sodium zeolite A with about 96% replacement of the sodium ions by potassium ions.

The sodium zeolite A, conveniently synthesized from .sodium aluminate, sodium silicate and water, has a larger pore size than potassium zeolite A. The activated sodium zeolite A adsorbs water readily and adsorbs in addition somewhat larger molecules. For instance, at liquid air temperatures it adsorbs oxygen but not appreciable amounts of nitrogen as shown below for a typical sodium zeolite A sample.

Partial Weight per- Adsorbate Temperapressure cent ture 0.) (mm. Hg) adsorbed on Na A Oxygen 196 100 24.8 Nitrogen 196 700 0. 6

Zeolite A may be used to separate oxygen from mixtures of oxygen and other gases such as krypton, xenon and methane whose molecules are larger than oxygen. Neon, hydrogen and helium having molecules small enough to permit adsorption, may also be separated from oxygen with zeolite A since their boiling points are L so low that no appreciable adsorption occurs at the "temperature of liquid air. An important property of zeolite A is the change in its sieving characteristics, particularly its selectivity, with changes in temperature. At liquid air temperatures, about -196 C., oxygen but no substantial amount of nitrogen is adsorbed. At higher temperatures, about -75 C. or higher, nitrogen is adsorbed in larger quan- 14 titiestlian-"bx ygeri. This behavior the following data:

is -derrio nstratetl by The preferential adsorption of nitrogen from air at 78" C. was also demonstrated in a flow system in which air at 78 C. and atmospheric pressure was passed over a bed of sodium zeolite A pellets with a superficial contact time of 25.6 seconds. The oxygen content of the exit gas rose as high as 89%, and the sorbed gas was as high as 94% nitrogen. With a short contact time of 2 to 7 seconds the first gas emerging from the bed was nitrogen'as a result of the more rapid rate of oxygen adsorption on freshly ac tivated zeolite at -78 C. This, however, is a temporary condition which changes as the zeolite A approaches its capacity for oxygen at that temperature;

This inverse temperature eifect was found to be quite pronounced in the case of butene-l. At 0 C. the adsorption of butene-l on zeolite A is-low but as the temperature is raised the adsorption increases as it more freely diffuses into the pores of the zeolite. At still higher temperatures the adsorption again decreases. The data are tabulated below al-ongwith-similar datafor ethane to showhow the selectivity of sodium zeolite A for these two'gases is temperature dependent.

' Weight percent Adsorption adsorbed Adsorption temp. 0.) press.

(mm. Hg)

Butane-1 Ethane At about room temperature the sodium zeolite A a'dsorbs the C and C members of the straight chain saturated hydrocarbon series but not appreciable amounts of the higher homologs. Typical results are shown below.

Weight Adsorbate Tempere- Pressure percent ture 0.) (mm. adsorbed on NflgA Methane 25 700 1". 6 Ethane 25 700 7.4 Propane 25 700 0. 7 Butane"--. 25 132 0. 9 Octane 25 12 0. 5

This data suggests a process of using sodium zeolite A to remove methane and ethane from mixtures with propane and higher homologs of the series and with other larger molecules not appreciably adsorbed or with other gases less strongly adsorbed. The maximum dimension of the minimum projected cross-section for ethane is 4.0 A. and for propane 4.9 A. The sodium zeolite A adsorbs the former but not appreciable amounts of the latter.

In the series of straight chain unsaturated hydrocarbons, the C and 0;, molecules are adsorbed but the higher homologs are only slightly adsorbed. is

shown in the-data, :below for a typical sodium, zeolite A.

An exception is butadiene, a doubly unsaturated C Weight Weight Adsorbate Tempera- Pressure percent 5 Adsorbate Tempera- Pressure percent ture 0.) (mm. Hg) adsorbed ture 0.) (mm. Hg) adsorbed on N 82A on CaA Ethylene 200 196 100 30. 7 Propylene. 25 200 196 700 23. 9 Butene-l- 25 200 196 0.007 15. 2 Butadlene 25 9 This sieving action toward unsaturated hydrocarbons permits the. separation. of the smaller, shorter, lower molecular Weight unsaturates such as ethylene, acetylene, ,propylene and the doubly unsaturated C hydrocarbons from the larger, longer, heavier unsaturated and saturated hydrocarbons that are not appreciably adsorbed, or only weakly adsorbed and from gases that are only weakly .adsorbed becauseof their low boiling points, such as 0 molecules, such as, carbon tetrachloride, acetone or the cyclic hydrocarbons having four or more atoms in the ring, such as benzene, toluene, cyclohexane and methyl cyclohexane. This behavior of sodium zeolite A permits the separation of methanol, ethanol and propanol from longer chain normal alcohols, iso-alcohols, secondary alcohols, tertiary alcohols, cyclic hydrocarbons having four or more atoms in the ring, and all molecules whose maximum dimension of the minimum projected crosssection is as great as or larger than that of propane. Small molecules like carbon monoxide, ammonia, carbon dioxide, sulfur dioxide, hydrogen sulfide, oxygen and nitrogen are all adsorbed at room temperature on sodium zeolite A.

In borderline cases where adsorbate molecules are too large to enter the pore system of the zeolite freely, but are not large enough to be excluded entirely, there is a nfinite rate of adsorption and the amount adsorbed will materials with larger pores than exist in sodium zeolite These two .forms of divalent ion exchanged zeolite A behave quite similarly and adsorb all molecules adsorbed by sodium zeolite A plus some larger molecules. For instance, in addition to adsorbing oxygen at liquid air temperature,,,-nitrogen and krypton are also adsorbed. Typigcal, data for an. 85% exchanged calcium zeolite A, pre- 1 This data obtained on a 66% Ca exchanged zeolite A.

At room temperature, long straight chain saturated and unsaturated hydrocarbons and alcohols are adsorbed by calcium and magnesium zeolite A but no appreciable amounts of branched chain molecules or cyclic molecules having four or more atoms in the ring are occluded. Typical data for magnesium and calcium exchanged zeolite A are given below.

N H CO and CH and from molecules that are .too 20 large to be adsorbed such as the cyclic molecules having Weight Weight Temp. Press Percent Press Percent four .or more atoms in the ring. Adsorbate Q) (mm (mm In the, straight cham alcohol series the C C and Hg) sorbed Hg) sorbed C homologs are adsorbed by sodium zeolite A but 25 MA on 03A longer ones .are only slightly adsorbed as typical data P 95 410 11 1 nropane .6 350 1.2 shown below luustratesn-Butane-.. 25 132 12.9 132 13.2 n-He 25 31 14. 1

n-Heptane- 25 26 16.6 45 16. 5

. We ht nane 25 11 12.3 11 15.4

.Adsorbate Tempera- Pressure percent Mariti e." 25 126 0.1 126 0.1

e( -Hg) a sorbed 30 i-Penta11e. 25 126 0.1 126 0.1

on N 22A n-Propanoln. 25 7. 5 18. 8 7. 5 17. 7

v n,-Butano1 25 13 17.0 13 19.4 i-PropauoL, 25 36 .0. 3 36 0. 8 Methanol.. 25 13 20-0 l-Butanol 25 12 1. 2 12 1. 8 Ethanol..." 25 7 18-0 2-butanol 25 15 1.1 15 3.17 n-Propanolu 5 12 8 Buteuc-l. 25 57 14. 1 57 12.7 n-Butanol V 25 7 1.8 35 ,Butene-Z- 25 127 10.9 127 14.9 i-Butene. 25 O. 3 90 0. 1

' Carbon tetrachlo- Branch chain molecules, for example iso-butane and g8 3'3 iso-butanol, are not appreciably adsorbed by sodium 'm-Xylene s 0.0 zeolite A not are secondary alcohols, such as iso-propyl alcohol and secondary butanol, nor are other larger 40 Benzene 5.5 Propane 4.9 Ethane 4.0 Iso-butane 5.6

Thus calcium and magnesium zeolite ,A may be used for the separation of mixtures of straight chain and branched chain molecules, or for separation of straight chain molecules from cyclic compounds having four or more atoms in the ring.

Calcium and magnesium exchanged zeolite A have not only larger pores, as evidenced by their sieving action, but the total pore volume available per gram of adsorbent to a small molecule like Water is greater in calcium and magnesium zeolite A than it is in sodium or p-otassiumzeolite A.

A unique characteristic of calcium and magnesium. exchanged zeolite A is that the opening of the pore to molecules larger than can be adsorbed by sodiumzeolite A does not occur gradually as the sodium ions are replaced by calcium ions but rapidly ,in a narrow range of composition. When exchange is only 25% or less complete, the material has the sieving characteristics of sodium zeo- .lite A, butwhen, exchange is 40% complete, or more,

1.7 of heptane adsorbed on. a sodium zeolite A sample part1ally exchanged with calcium is tabulated below "as a function of the completion of exchange.

There are numerous other ion exchanged forms of zeolite A such as lithium, ammonium, silver, zinc, nickel, hydrogen, and strontium. In general, the divalent ion exchanged materials such as zinc, nickel, and strontium zeolite A have a sieving action similar to that of calcium and magnesium zeolite A, and the monovalent ion exchanged materials such as lithium and hydrogen zeolite A behave similarly to sodium zeolite A, although some difterences exist.

The molecular sieving characteristics of zeolite A may be influenced by the temperature and pressure at-which the adsorbent is activated, as shown by oxygen adsorption data for sodium zeolite A.

Weight percent adsorbed on N MA at 1S16 O. and 13 mm. Hg pressure Activation temperature (pressure 0.01 mm. Hg.)

The sample of sodium zeolite A activated at the lower temperature does not adsorb oxygen while the sample activated at the higher temperature does. This is true even though both samples adsorb over 24% by weight of water at 25 C. and 24 mm. of Hg water vapor pressure.

Similarly, the sieving characteristics of zeolite'A may be altered by partially loading an activated sample with water. For example, a particular sample of sodium zeolite A adsorbed 8% ethane at 25 C. and 500 mm. of mercury pressure. Yet, when 7% by weight water was added to the activated sample, its ethane adsorption under the same conditions of temperature and pressure was reduced to less than one-tenth its former capacity. Similar altering of the sieve efiect can be eifected with partial loading with other adsorbates. 1 i

The molecular sieving characteristics of zeolite A can be employed in numerous processes for the separation of mixtures composed of one or more molecular species of such a size and shape as to be adsorbed and one or more species of molecules too large to be adsorbed. For instance, one and one-half grams of sodium zeolite A activated at 350 C. at a pressure equal to-or less than 10 microns was put into a 2 /2 grams liquid mixture whose composition was 89.6% benzene and 10.4% ethanol. The solution which was at 25 C. before the addition became warm to the touch. When adsorption was complete analysis showed the liquid phase to be purebenzene, the ethanol having been adsorbed on the zeolite to the extent of 17.3%by weight. I

Another unique property of zeolite A is its strong preference for polar, polarizable and unsaturated molecules, providing of course that these molecules are of a size and shape permitting them to enter the pore system of the 'zeolites. This is in contrast to charcoal and silica gel which show a main preference based on the volatility of the adsorbate. The following table compares the adsorptionsof water, a polar molecule, G0,, a polarizable molecule, and acetylene, an unsaturated molecule on ch'arcoaL' silica 'gel and sodium zeolite A. The table illustrates the high capacity the zeolite'A has for polar, polarizable and unsaturated molecules.

Tem- Weight percent adsorbed Adsorbate Pressure pcra- (mm. ture Hg) C.) Na A Charcoal Silica gel 0.2 25 22.1-- 0. 1 1. 6 50 25 15. 3 2. 2 1. 3 Acetylene 50 25 9. 5 2. 5 2. 1

The selectivity of the sodium zeolite A for polar over non-polar molecules is shown by adsorption data for the polar carbon monoxide molecule and the non-polar oxygen molecule at 75 C.

Weight percent adsorbed at 500 mm. Hg pressure Adsorbate Oxygen 6. 5 Carbon monoxide 11. 5

Tem- Weight percent adsorbed peraon N 84A Pressure (mm. Hg) (gue) CzHo 2 02H:

Weight percent adsorbed on OaA a e CsHt wow These data, indicating strong adsorption for the unsaturated molecules, show that unsaturated molecules may be separated from saturated molecules or less unsaturated molecules even though all are of approximately the same size and small enough to enter the pore system of zeolite A. Specifically, it shows a propensity for separating acetylene from both ethylene and ethane and from other saturated hydrocarbons, such as methane and propane, and from molecules that are less strongly adsorbed because of their low boiling points, such as nitrm gen, oxygen, hydrogen, and carbon monoxide.

A selectivity for polar, polarizable and unsaturated molecules is not new among adsorbents. Silica gel exhibits some preference for such molecules, but the extent of this selectivity is so much greater with zeolite A that separation processes based upon this selectivity become feasible. For example, it a sample of activated sodium zeolite A is brought to equilibrium at one atmosphere of pressure and 25 C. with a gas mixture composed of 20% ethylene and ethane, the adsorbed phase con-' tains more than six times as much ethylene as'ethane i Silica gel on the other hand has more ethane than ethyl ene in the adsorbed phase under similar conditions.

The selectivity for polar, polarizable and unsaturated molecules can be altered appreciably by ion exchange and in addition relative selectivities may change with tem- 1,9 perature. Such effects are illustrated with the. small rbon monoxide molecule on sodium, calcium and magneslum zeolite A at -75, C. and, 0. C.

Weight percent 00 Adsorbed at. 700 mm. Adsorbent Hg Zeolite A shows a selectivity for adsorbates', provided that they are small enough to enter theporous network of the zeolites, based on the boiling points of the adsorbates, as well as on their polarity, polarizability or degree of unsaturation. For instance, hydrogen which has a low boiling point is not strongly adsorbed at room temperature. A non-polar saturated ethane molecule is somewhat more strongly adsorbed at room temperature than the polar carbon monoxide molecule because the effect of the much lower boiling point or carbon {11011-- oxide, 192 C. as compared. to 88 C. for ethane, more than counterbalances the polarity eifect.

A further important characteristic of zeolite A is its property of adsorbing large amounts. of adsorbates, at low adsorbate pressures, partial pressures or concentra tions. This property makes, zeolite A uniquely useful in the more complete removal of adsorbable impurities from gas and liquid mixtures. It gives them a relatively high adsorption capacity even when. the. material being adsorbed from a. mixture is present in very low concentrations, and permits the-efficient recovery of minor com ponents of mixtures. This characteristic is all the more important since adsorption processe are most frequently used when the desired component is present in low concentrations or low partial pressures. High adsorptions at low pressures or concentrations on zeolite A are illustrated in the following table, along with some comparative data for silica gel and charcoal.

Tem- Presperature Weight percent adsorbed Adsorbate Nam CaA MgA Charcoal gel NHa 1 Po=the vapor pressure of water at the temperature given.

The strong adsorption of water by zeolite at low pressures can be capitalized on to remove water from mixture with other materials. The high adsorptive. ca

pacity by zeolite A for carbon dioxide as compared to that for carbon monoxide, oxygen, nitrogen, hydrogen,

methane, and ethane renders zeolite A suitable for use 5 in the separation of carbon dioxide from mixtures with these gases. Similarly hydrogen sulfide, sulfur dioxide, and ammonia may be separated by zeolite A from mixtur'es of these gases with oxygen, nitrogen, hydrogen, carbon monoxide, and carbon dioxide.

The adsorption capacity of adsorbents usually decreases With increasing temperature, and while the adsorption capacity of an adsorbent at a given temperature may be sufficient, the capacity may be wholly unsatisfactory at a higher temperature. With zeolite A a relatively high capacity may be retained at higher temperatures. For instance, adsorption data for water on, calcium. zeolite A and silica gel at 25 C. and 100 C. are, tabulated below, It is seen that the capacity of calcium, zeolite. A remains high even at 100 C.

Weight; percent adsorbed at 0. Pressure (mm Pressure (Min.

Silica CaA Silicav OaA gel gel Po=the vapor pressure of water at 25 C.

Zeoli'teA may be. activated. by heating it in either air, a vacuum, or other appropriate gas to temperatures of as high as 600 C. The conditions used for desorption of an adsorbate from. zeolite A vary with the adsorbate, but either raising the temperature and reducing the pressure, partial pressure or concentration of the adsorbate in contact with the adsorbent or a combination of these steps, is usually employed. Another method is to displace the adsorbate. by adsorption of another more. strongly held adsorbate. For instance, carbon monoxide adsorbed. ona bed of zeolite A at 25 C. has been displaced by' the adsorption of either carbon dioxide or acetylene at 25 C.

ZeoliteA may be-used as an adsorbent for the purposes indicated above in: any suitable form. For example, a Column of, powdered crystalline material has given excellent results as hasa pelleted formjobtained by pressing into, pellets-a mixture of zeoliteA and, a suitable bonding agent suchv as: day.

What iszclairncd is:-

1'. A crystalline synthetic material having a composition expressed in terms of oxides as follows:

wherein M represents at least one of the materials in the groupv consisting. ofhydrogen, ammonium, metals in groups. I andII. of the periodic table, and the transition metals of;the periodic table, n represents the valence of MJ and Y maybe any value up to about 6, the atoms of said material being arranged in a unit cell in such. a. manner that the X-ray powder difiraction pattern ofthe material is essentially the same as that shown in Table A..

2. A crystalline synthetic material having a composition expressed in terms of oxides as follows:

wherein, M. represents at least one of the materials inthejgroupconsisting of hydrogen, ammonium, metals in. groups I. andII of the periodic table, and the transition metals. of the periodic table, n represents the valence offMJ. and. Y may be any value up to. about. 6,; the atoms of said material being arranged in a unit cell in such a. manner that the X-ray powder diffraction pattern of'the material is essentially the same as that shown in Table B.

3. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder diffraction pattern of the silicate is essentially the same as that shown in Table A for sodium zeolite A.

4. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder difiraction pattern of the silicate is essentially the same as that shown in Table B.

5. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder difiraction pattern of the silicate is essentially the same as that shown in Table A, at least a portion of the sodium ions in the silicate being replaced by at least one of the cations in the group consisting of hydrogen, ammonium, metals in groups I and II of the periodic table, and the transition metals of the periodic table.

6. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder diffraction pattern of the silicate is essentially the same as that shown in Table B, at least a portion of the sodium ions in the silicate being replaced by at least one of the cations in the group consisting of hydrogen, ammonium, metals in groups I and II of the periodic table, and the transition metals of the periodic table.

7. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder diiiraction pattern of the silicate is essentially the same as that shown in Table A, at least a portion of the sodium ions in the silicate being replaced by calcium.

8. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder difiraction pattern of the silicate is essentially the same as that shown in Table B, at least a portion of the sodium ions in the silicate being replaced by calcium.

' 9. Crystalline synthetic sodium aluminum silicate the atoms of which'are arranged in a unit cell in sucha manner that the X-ray powder diffraction pattern of the silicate is essentially the same as that shown in Table A, at least a portion of the sodium ions in the silicate being replaced by potassium.

10. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder diffraction pattern of the silicate is essentially the same as that shown in Table B, at least a portion of the sodium ions in the silicate being replaced by potassium.

11. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder diffraction pattern of the silicate is essentially the same as that shown in Table A, at least a portion of the sodium ions in the silicate being replaced by magnesium.

12. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder difiraction pattern of the silicate is essentially the same as that shown in Table B, at least a portion of the sodium ions in the silicate being replaced by magnesium.

13. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder difiraction pattern of the silicate is essentially the same as that shown in Table A, at least a portion of the sodium ions in the silicate being replaced by hydrogen.

14. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a man 22 ner that the X-ray powder difiraction pattern of the silicate is essentially the same as that shown in Table B, at least a portion of the sodium ions in the silicate being replaced by hydrogen.

15. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder difiraction pattern of the silicate is essentially the same as that shown in Table A, at least a portion of the sodium ions in the silicate being replaced byammonium.

16. Crystalline synthetic sodium aluminum silicate the atoms of which are arranged in a unit cell in such a manner that the X-ray powder diffraction pattern of the silicate is essentially the same as that shown in Table B, at least a portion of the sodium ions in the silicate being replaced by ammonium.

17. A crystalline synthetic metal-aluminum-silicate the sodium exchanged form of which has a composition expressed in terms of oxides as follows:

wherein Y may be any value up to about 5.1, said sodium exchanged form of said silicate having an arrangement of atoms such that the X-ray powder diflraction pattern of the silicate is essentially the same as that shown in Table A for sodium zeolite A, said exchanged form of said silicate being further characterized in that at a temperature of about 196 C. the dehydrated crystal adsorbs substantial quantities of oxygen but less than about 2% by weight oi nitrogen.

18. A crystalline synthetic metal-aluminum-silicate the sodium exchanged form of which has a composition expressed in terms of oxides as follows: 1

the calcium exchanged form of which has a composition expressed in terms of oxides as follows:

1.0i0.2CaO:Al O :1.85i0.5SiO :YH O

wherein Y may be any value up to about 5, said calcium exchanged form of said silicate having an arrangement of atoms such that the X-ray powder difiraction pattern of the silicate is essentially the same as that shown in Table A for calcium zeolite A, said exchanged form of said silicate being further characterized in that at a temperature of about 25 C., the dehydrated crystal absorbs substantial quantities of butane but less than about 2% by weight of iso-butane.

20. A crystalline synthetic metal-aluminum-silicate the calcium exchanged form of which has a composition expressed in terms of oxides as follows:

wherein Y may be any value up to about 5, said calcium exchanged form of said silicate having an arrangement of atoms such that the X-ray powder diffraction pattern of the silicate is essentially the same as that shown in Table B for calcium zeolite A, said exchanged form of said silicate being further characterized in that at a temperature of about 25 C., the dehydrated crystal adsorbs substantial quantities of butane but less than about 2% by weight of iso-butane.

21. Method of preparing a sodium-aluminum-silicate having atoms arranged in a unit cell in such a manner that the X-ray powder diffraction pattern of the silicate is 23 ss t lly the sam as hat shc n. in Table A, hich comprises preparing a sodium-a1urninumasilicate water mixture whose composition, expressed in terms of oxidemole ratios, falls with the ranges:

Na O/SiO ratio from 1.0 to. 3.0 and a H O/Na O ratio from 35-200 when the SiO /Al O ratio is from 0.5 to 1.3; a NaO/SiO ratio from 0.8 to 3.0 and a H O/Na O ratio from 35 to 200 when the SiO /Al O ratio is from 1.3 to 2.5;

maintaining the mixture at a temperature within the range. from about 20 C. to 175 C. until crystals as previously defined are formed; and separating the crystals from the mother liquor.

22. Method of preparing a sodium-aluminum-silicate having atoms arranged in a unit cell in such a manner that the X-raypowder diffraction pattern is essentially the same as that shown in Table B, which comprises prep g a edium-alum num i icate water. mixture who e composition, expressed in terms of oxide-mole ratios, falls with the ranges:

Na O/SiO ratio from 1.0 to 3.0 and a I-I O/Na O ratio from 35-200 when the Si O /Al O ratio is from,0.5 to 1.3 a Na O/SiO ratio from 0.8 to 3.0 and a H O/Na O ratio from 35 to 200 when the. SiO /Al O ratio is from 1.3 to 2.5;

maintaining the mixture at a temperature within the range from about 20 C. to 175 C. until crystals as previously defined are formed; and separating the crystals from the mother liquor.

23. Method of preparing a sodium;aluminum-selicate having atoms arranged in a unit cell in such a manner that the X-ray powder ditiraction pattern of the silicate is essentially the same as that shown in Table A, which comprises preparing asodium-aluminum-silicate water mixture whose composition, expressed in terms of oxidemole ratios, falls with the ranges:

Na O/SiO ratio from 1.0 to 3.0 and a H O/Na O ratio from 35-200 when the SiO /Al O ratio is from 0.5 to 1.3;

Na O/SiQ ratio from 0.8 to 3.0 and a H O/Na O ratio from 35 to 200 when the SiO /Al O ratio, is from. 1.3 to 2.5,;

maintaining the-mixture at a temperature-within the range from about 20- C. to C. until crystals as previously defined are formed; and separating the crystals from the mother liquor.

References Cited in the file of this patent; UNITED STATES PATENTS 1,682,588 Wietzel Aug. 28, 1928 1,906,203 Bruce Apr. 25, 1933 2,137,605 Derr Nov. 22, 1938 2,306,610 Barrer Dec. 29, 1942 2,413,134 Barrer Dec. 24, 1946 2,512,053 Calmon June 20, 1950 2,617,712 Bond Nov. 11, 1952 FOREIGN PATENTS 574,911 Great Britain Ian. 25, 1946 OTHER REFERENCES:

Mellon: Comprehensive Treatise: on Inorganicv and Theoretical Chemistry, vol. 6, 1925, pages 567, 568, 576-579, Longmans, Green and Co., N.Y., N.Y.

Synthesis, of Zeolitic Mineral, Barrer, ChemicalSociety Journal, London, 1948, pages 127-143.

Barrer et al.: The Hydrothermal Chemistry'of Silicates, part II, Article in the Journal of Chemical Society, 1952, pp. 1561-1571.

Physical Chemistry of the Silicates, Eitel, University of Chicago Press, 1954, pages 994-1021. 

1. A CRYSTALLINE SYNTHETIC MATERIAL HAVING A COMPOSITION EXPRESSED IN TERMS OF OXIDES AS FOLLOWS: 